Deck railing and baluster calculator

Space balusters evenly under the largest allowed gap, and count railing posts, balusters and rail length for each side of the deck.

Your measurements

Editable example

Use the unit shown for each box, or type another one: 12 ft 6 in, 150 in, 3.8 m and 600 mm all work, as do the marks on a tape measure.

Railing run 1

Run nameRun length along the deck edge (ft)Joins the previous runDistance to the stair opening (ft)Stair opening, post center to post center (ft)Use zero where there are no stairs.

Railing run 2

Run nameRun length along the deck edge (ft)Joins the previous runDistance to the stair opening (ft)Stair opening, post center to post center (ft)Use zero where there are no stairs.

Railing run 3

Run nameRun length along the deck edge (ft)Joins the previous runDistance to the stair opening (ft)Stair opening, post center to post center (ft)Use zero where there are no stairs.

Length unitsSwitches the main dimensions between feet and meters. Boxes in inches switch to millimeters, and you can pick another unit beside any of them. Areas, volumes and package sizes keep the units on their labels.Maximum post spacingAWC’s example deck guard shows posts at most 6 feet apart. Use your railing system’s figure.Gap must stay underAWC’s deck guide says openings must not let a 4-inch sphere through. Check your local code.

Package sizes, prices and materials

Post widthMeasure your post; the clear space between posts is what the balusters fill.Baluster widthRails per bayYour price per baluster ($)

Example: replace these measurements

Your material list

72 balusters

Shopping list & save options

Railing length: 36 ft
Stair openings: 4 ft
Total posts: 8
End posts: 2
Corner posts: 2
Gate or stair posts: 2
Grade-change posts: 0
Line posts: 2
Bays: 6
Bay type 1 (6 bays): 68.5 in clear · 12 balusters · 3.88 in gaps · mark every 5.38 in
Rail length: 68.5 ft for 2 rails per bay
Baluster subtotal: Add your price

Gaps are equal within each bay. Check the finished gaps with a 4-inch sphere or block before fixing the last baluster.

Post layout for the selected run. A dashed opening is the stair opening. Dense runs show fixed posts only.

The calculation

floor((68.5 − 4) ÷ (1.5 + 4)) + 1 = 12 balusters; (68.5 − 12 × 1.5) ÷ 13 = 3.88 in gaps
72 balusters across 6 bays

Before ordering, use the tile measurement, layout & overage handoff guide to check the inputs and take the right questions to the supplier. Choose another calculator.

How to plan the quantity

Enter each side of the deck that needs a railing, measured along the edge. Runs that meet at a corner share the corner post. Leave a stair opening by entering its distance from the start of the run and the distance between the two stair posts.

Each run is split into equal bays no longer than your maximum post spacing. In each bay, the balusters are spaced evenly so the gap between them, and between a baluster and a post, stays under your limit. The list gives the gap and the on-center mark spacing, so you can mark every baluster before fixing it.

Rail length is the clear space between posts, times the rails in each bay. Cut lengths depend on how your rails fix to the posts.

Before you order

This spaces balusters and counts parts. It does not size posts, choose connectors or approve a guard; AWC’s guide and your local code set how guard posts are attached.
Stair railings follow the stair slope and need their own layout.

Common questions

How far apart should deck balusters be?

Close enough that a 4-inch sphere cannot pass between them, the rule in the American Wood Council’s DCA 6 deck guide. The calculator spaces them evenly so every gap stays under your limit.

Source: AWC DCA 6 deck guide: guard requirements. Listed on the Sources page.

How many balusters per foot of railing?

A little over two. With 1 1/2-inch balusters and gaps just under 4 inches, each baluster and gap take about 5 1/2 inches.

How far apart should railing posts be?

The American Wood Council’s example deck guard shows posts at most 6 feet apart. Railing systems set their own spacing, so use yours.

Source: AWC DCA 6 deck guide: Figure 24, example guard detail. Listed on the Sources page.

When does a deck need a railing?

The American Wood Council’s guide says decks more than 30 inches above grade need a guard. Check your local code.

Source: AWC DCA 6 deck guide: guard requirements. Listed on the Sources page.